The present invention is an improved process for hydrosilating alkynes with hydridosilanes in the presence of a platinum catalyst selected from a group consisting of platinum halides and the reaction product of platinum halides with organosilicon compounds having terminal aliphatic unsaturation. The process uses a cycloalkadiene comprising about six to 20 carbon atoms as a catalyst modifier to reduce formation of the bis-silated adduct of the alkynes.
Virtually any compound which contains a .ident.SiH group can be reacted with compounds containing aliphatic unsaturation in the presence of a platinum compound such as chloroplatinic acid to effect a reaction typically referred to as hydrosilation or hydrosilylation. Speier et al., U.S. Pat. No. 2,823,218, discuss such hydrosilation reactions in detail.
Willing, U.S. Pat. No. 3,419,593, describes a group of catalysts that are the reaction product of chloroplatinic acid with organosilicon compounds having terminal unsaturation that are particularly useful in many such hydrosilation processes.
Lindner et al., U.S. Pat. No. 4,292,434, describe a hydrosilation catalyst obtained by dissolving a platinum halide in at least 20 parts by weight of an olefin, such as 1,5-cyclooctadiene, for each part by weight of platinum halide and subsequently heating and mixing the solution obtained with from 0.5 to one mole of a primary or secondary amine for each gram atom of platinum. The catalyst is described as useful in the reaction of acetylene with methyldichlorosilane to produce vinylmethyldichlorosilane.
A common problem associated with the hydrosilation of an alkyne with a hydridosilane in the presence of a platinum halide or platinum olefin complex as catalyst is the formation of the bis-silated adduct of the alkyne as a by-product. Typically such hydrosilation processes are run under high pressure to increase the concentration of alkyne in the reaction mixture relative to the alkenyl substituted product thereby minimizing the formation of the bis-silated adduct. However alkynes such as acetylene are explosive at high pressures, thereby making such processes dangerous. The present inventors have discovered that in processes where an alkyne is silated with a hydridosilane in the presence of a platinum catalyst selected from a group consisting of platinum halides and reaction product of platinum halide with organosilicon compounds having terminal aliphatic unsaturation, the presence of about 0.1 to 5 moles of cycloalkadiene comprising about six to 20 carbon atoms per g.multidot.atom of platinum can reduce the amount of the bis-silated adduct formed. This can allow such processes to be run at near normal atmospheric pressure while still providing for an acceptable ratio of alkenyl substituted product to bis-silated by-product.